Surprise tornadoes and mesoscale accidents, "oddball" events. Why do they happen?

[WeathermanLeprechaun]

This thread is for the purpose of something I've found extremely intriguing the last few months. We know the usual characteristics of tornado outbreak with strong low level shear. But what about those surprise, photogenic tornadoes nobody expected? Like Wellfleet, Floyd, Chapman. Why do these tornadoes happen? Their environments are unusual

I plan to use this thread as a case study of such environments and to detail the trend I've noticed. These events typically favor big time, surprise, photogenic tornado events but they rarely ever work out. The recurrence interval is sporadic.

The environments typically consist of
Large amounts of vertical instability
0-3km shear of 25+ adequate for supercells.
SE moving supercells, stationary or anchored along boundaries
Often impressive yet dry PBLs that don't force excess production

Every time a environment such as this comes around, i will note it in this thread

One of these environments happened in SE MT months back, and didn't produce. Why do these same environments produce, yet other times they don't work. So many variables and subtle differences in these cases that I want to find out. That's why this thread is made.

 

[N0mz]

I would add 3cape and surface vorticity. Mesoanalysis has a combined field of these two because they are so good at picking up mesoscale setups.

 

[WeathermanLeprechaun]

I would add 3cape and surface vorticity. Mesoanalysis has a combined field of these two because they are so good at picking up mesoscale setups.

Yeah, sure, surface vorticity

Floyd and Wellfleet didn't rally exhibit low level instability of sorts, those storms moreso experienced very large vertical instability and vertical stretching from boundaries and etc. I think a lot more goes into these shock tornadoes than we think

 

[N0mz]

Yeah, sure, surface vorticity

Floyd and Wellfleet didn't rally exhibit low level instability of sorts, those storms moreso experienced very large vertical instability and vertical stretching from boundaries and etc. I think a lot more goes into these shock tornadoes than we think

I also think hitting the boundary at the right angle plays a large role. Obviously you need to be on the warm side of the boundary, but I think the manner with which the updraft and boundary collide is very important. Maybe similar to how cell mergers work; I think most people with enough radar experience can pretty accurately predict which cell mergers will be productive/destructive just based on how the cells are colliding. Obviously though, forecasting this from more than ~2 hours out is pretty much impossible.